1. Field of the Invention
The present invention relates generally to giant magnetoresistive (GMR) read head sensors for magnetic heads, and more particularly to improved CPP sensor structures in which Heusler alloys are utilized.
2. Description of the Prior Art
A hard disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk, where the magnetic head, or heads, read from or write data to concentric data tracks defined on surface of the disks. The goal in recent years is to increase the amount of data that can be stored on each hard disk. Increasing the areal data storage density of the disks can be accomplished by reducing the size of data bits, such that the number of tracks per inch (tpi) and bits per inch (bpi) on the data tracks on the disk can be increased. However, to read data from a disk with an increased bpi, it is also necessary to develop a sufficiently sensitive sensor structure with reduced noise within the read head of the magnetic head, such that data bits can be detected and read.
A read head typically includes a giant magnetoresistive (GMR) spin valve sensor structure for reading the data from the disk of the hard disk drive. As is well known to those skilled in the art, such GMR sensor structures include a plurality of thin film layers disposed between two magnetic shields that define the read gap. The thin film layers have particular magnetic properties, and are sensitive to the magnetic field of the data bits on the hard disk. Thus, more sensitive sensor layers with lower noise characteristics disposed between the two magnetic shields allow the read head to detect the smaller data bits that a higher bpi data track contains.
The thin film layers of a typical GMR spin valve sensor will include at least a reference magnetic layer, a non-magnetic spacer layer, and a free magnetic layer. In operation the magnetic moment of the free layer is free to rotate within the layer with respect to the ABS from a quiescent or zero bias point position in response to magnetic flux from data bits located on the rotating magnetic disk. For read head applications the magnetization of the reference layer is typically fixed in a directed substantially perpendicular to the ABS, while the direction of the free layer is typically directed substantially parallel to the ABS. In the following description, substantially parallel means closer to parallel than perpendicular, substantially perpendicular means closer to perpendicular than parallel.
There are generally two ways to provide sense current to the read head. The older way is by supplying a current that runs longitudinally in the plane of the ABS from one side of the free magnetic layer to the other side. A more recent design is to supply the sense current perpendicularly to the plane (CPP) of the central layer stack, that is, between the magnetic shields. In such CPP head designs the magnetic shields are typically used as the electrical leads and the sense current flows through the various layers of the sensor that are disposed between the magnetic shields.
When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve sensor employs an antiparallel (AP) pinned layer structure it is referred to as an AP-pinned spin valve. An AP-pinned spin valve includes first magnetic (AP1) and second magnetic (AP2) layers separated by a thin non-magnetic coupling layer such as Ru or Ir. The thickness of the coupling layer is chosen so as to antiparallel couple the magnetic moments of the first and second ferromagnetic layers of the pinned layer structure.
The magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material (AFM) such as PtMn, IrMn, or IrMnCr. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a net magnetic moment, when exchange coupled with a magnetic material, it can strongly pin the magnetization of a ferromagnetic layer. In an AP-pinned spin-valve the AP1 layer adjacent and pinned by the AFM is usually referred to as the pinned layer while the AP2 layer adjacent to the spacer layer is usually referred to as reference layer. In a simple spin-valve the pinned layer is also acting as reference layer. The following description will simply refer to the layer adjacent to the non-magnetic spacer layer (the AP2 in an AP-pinned spin-valve and the pinned layer in a simple spin-valve) as the reference layer. A spin valve sensor is also known as a top or bottom spin valve sensor depending upon whether the reference layer is at the top (formed after the free layer) or at the bottom (before the free layer).
In the ongoing efforts to identify magnetic and nonmagnetic sensor layer materials that can improve sensor performance, Heusler alloys have recently been demonstrated to provide improved sensor performance. A Heusler alloy has the chemical formula A2MnB, where A and B are metals or semiconductors. Recently, U.S. Pat. No. 6,876,522, issued Apr. 5, 2005 to Ambrose et al. has identified particular Heusler alloys that may be utilized for the reference magnetic layer, spacer layer and free magnetic layer of a GMR sensor. While the Heusler alloys identified in this patent provide improved sensor performance, there is a need for the identification and utilization of further Heusler alloys, not identified in this patent, that when used in appropriate combinations and sensor layer configurations provide still further enhanced performance for a GMR sensor.